Magnetization switching using topological surface states

Topological surface states (TSSs) in a topological insulator are expected to be able to produce a spin-orbit torque that can switch a neighboring ferromagnet. This effect may be absent if the ferromagnet is conductive because it can completely suppress the TSSs, but it should be present if the ferromagnet is insulating. This study reports TSS-induced switching in a bilayer consisting of a topological insulator Bi(2)Se(3) and an insulating ferromagnet BaFe(12)O(19). A charge current in Bi(2)Se(3) can switch the magnetization in BaFe(12)O(19) up and down. When the magnetization is switched by a field, a current in Bi(2)Se(3) can reduce the switching field by ~4000 Oe. The switching efficiency at 3 K is 300 times higher than at room temperature; it is ~30 times higher than in Pt/BaFe(12)O(19). These strong effects originate from the presence of more pronounced TSSs at low temperatures due to enhanced surface conductivity and reduced bulk conductivity.